Process for mono-halogenating and mono-nitrating the diels-alder diadduct of hexachlorocyclopentadiene and naphthalene



United States Patent The subject application is a divisional application based upon our co-pending application, Serial No. 65,285, filed October 27, 1960, now abandoned.

This invention relates to the halogenation of organic substances. More particularly, it is concerned with the bromination and iodination of a certain class of organic compounds, and most specifically to the Diels-Alder adduct of two molecules of hexachlorocyclopentadiene and one molecule of naphthalene;

In US. Patent No. 2,658,926 it is disclosed that two molecules of 'hexachlorocyclopentadiene may be added unsymmetrically to one molecule of naphthalene in a DielS-Alder (diene) synthesis. Improved methods for the bromination and iodina-tion of this adduct, hereinafter referred to as DHA, and the new compositions of matter obtained, constitute the essence of this invention.

A principal object of the invention is therefore a new and useful process for brominating and iodinating DHA.-

A further object of the invention is a process for brominating andiodinating DHA which incorporates all the reacting bromine and iodine into the DHA derivatives.

Another object of the invention is a process for brominating and iodinati-ng DHA under unusually mild and readily controllable temperature conditions.

Another object of the invention is a process for iodinating DHA to produce compounds hitherto unobtainable.

Still another object of the invention is a process for selectively controlling the brominat-ion and iodination of DHA to accomplish either monoor di-halogenation or, alternately, mono halogenation and mono-nitration.

The attainment of these and other objects of the invention, both as to process and to products resulting therefrom, will be readily understood from the disclosure of this specification and the appended claims.

Bromine and iodine differ markedly from fluorine and chlorine, the other members of the halogen family, not only in their physical state, but also in their chemical 'rea-ctivity. One factor doubtless responsible, in part, at

least, for the decreasing chemical activity in certain types of reactions is the decrease of the oxidation potential in the order of fluorine, chlorine, bromine, and iodine.

These differences in physical state and chemical reactivity have frequently made it necessary to employ circuitous or cumbersome methods for preparing brominated or iodinated aromatic com-pounds, where as the chlorinated analogues can be prepared directly with little difiiculty; in some cases it has not been possible to prepare the desired iodinat-ed compounds by presently known procedures.

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cannot be tolerated technically; the waste hydrogen bromide is therefore recovered and converted back to bromine for further use. The equipment necessary for the recovery, however, and the processing steps involved, add

to the cost of the brominated compound being produced.

Iodination of aromatic compounds frequently employs a two-phase system in which benzene or other organic solvent is the carrier for the aromatic compound to be iodin-ated, while the second phase comprises ordinary concentrated (70 percent) nitric acid which continuously oxidizes hydrogen iodide back to iodine and thus effects a pressure of cationic iodine which is considered to be the reactive species in the iodination reaction.

Such heterogeneous systems, however, tend to react slowly, and the elevated temperatures needed to effect a reasonable rate of reaction tend to produce excessive amounts of undesired nitration and oxidation byproducts. In such systems, also, polyiodination is especially d-ifiicult.

The process of our invention for the halogenation of DHA constitutes a signal improvement over previous methods in that the reaction proceeds in a single phase, at temperatures only very slightly above ambient; that by-product formation is held to a minimum; and that the reactions involved can be controlled and guided at the volition of the operator to yield the specific react-ion products desired.

The essence of our invention is our discovery that white turning (98 to 100 percent) nitric acid is miscible in all proportions with methylene chloride, and that this combination reagent is an ideal vehicle for either monoor dibrominating or iodin-ating DHA. Red fuming (112 to 114 percent) nitric acid may be used in place of the white fuming acid, but its added expense does not justify its use. Such solutions are excellent solvents for DHA. The solutions are stable, since methylene chloride is com- 1 p'letely immune to attack by the acid at the reaction temperatures involved. The solutions reflux at temperatures below 55 C., thus providing means for automatic low-temperature control. At the conclusion of the reaction, the solvent, unused acid and product may be recovered without important loss.

We have found in such a system that practically complete monobromination or mon-oiodination of DHA may be accomplished, With only trace nitration, and using substantially stoichiometric amounts of halogen, by employ- 1ng 'a nitric acid concentration in the methylene chloride not higher than about 3 molar. Where dibromination or di-iodination is desired, a slight excess of halogen over the stoichiometric amount is necessary, and a somewhat higher concentration of nitric acid is required. This may result in a not inappreciab le amount of nitration in addition to the desired hal-ogenation; but the loss thus entailed is always considerably less expensive than the costs which would have resulted from the use of any previous prepara tive method where such was available. Where both halogenati-on and nitration are definite objectives, the concentration of nitric acid is simply increased still further. The simplicity and flexibility of our process in these respects will be seen in the examples given hereinafter.

Not only are the halogenated derivatives of DHA produced by our process of value in themselves but they are also intermediates in the preparation of other substances of potential commercial importance, e.g. dyestuif materials and pesticides. One of the most useful methods of further processing these halogenated derivatives of DHA is to subject them to pyrolytic cracking in a wipedfilm molecular type still, as will be described in greater detail in connection with the examples. This pyrolysis results in the formation of the corresponding halogenated naphthalenes and the regeneration of hexa-chlorocyclopentadiene, both of which products may readily be separated and recovered.

The application to actual practice of the principles of our invention set forth in the foregoing discussion is illus trated by the following examples, which are obviously given for purposes of illustration, not of limitation.

EXAMPLE 1 Monobromination of DHA 1795 grams of methylene chloride was placed in a 4-liter resin kettle equipped with mechanical stirrer and double reflux condensers. To this was added 674 grams (1 mole) of DHA, all of which did not go into solution at once. Next, 84 grams (about 0.525 mole) of bromine was introduced; and finally 183 grams of white fuming nitric acid (99 percent) was added resulting in a 2 molar acid concentration with respect to methylene chloride. The mixture was refluxed for 16 hours at 43 to 45 (2.; there was-a copious evolution of nitrogen oxides. At the end of 16 hours, 112.5 grams more of white fuming nitric acid was added, bringing up the calculated original acid concentration to 3 molar with respect to methylene chloride. Refluxing was continued for an hour. The reaction mixture was then distilled, to remove nearly all of the methylene chloride and nitric acid, which were recovered for reuse. The reaction mixture was then washed by shaking with an aqueous solution of sodium bisulfite to neutralize any residual bromine, then washed with water, and finally distilled to remove the remaining methylene chloride, and filtered. The residual product consisted of 720 grams of mono-bromo-DHA, pure but for trace amounts of DHA and nitro-DHA, with a yield equivalent to 95.5 percent of the theoretical.

EXAMPLE 2 Dibromination of DHA 898 grams of methylene chloride was placed in a 2-liter resin kettle fitted with double reflux condensers and mechanical stirrer. To this was added 337 grams (0.5 mole) DHA. Next, 8 8 grams (0.55 mole) of bromine was introduced and, finally, 91.5 grams of white fuming (99 percent) nitric acid, resulting in a 2 molar acid solution. The mixture was heated at reflux temperature (43 to 45 C.) for 16 hours. At the end of this time 55.5 grams more of nitric acid Was added, bringing the calculated acid concentration up to 3 molar; and the mixture was then refluxed for 1 hour, at the end of which time the calculated acid concentration was increased to'6 molar by adding 193.5 grams more of nitric acid. Heating at reflux temperature was then continued for hours. The reaction mixture was then worked up according to the procedure described in Example 1 above. The residual product recovered consisted of 247 grams of pure solid dibromo- DHA which crystallized from solution, corresponding to a yield of 59.4 percent of the theoretical (based on the weight of the DHA employed), and, in addition, 117 grams of mother liquor containing mostly dibromo-DHA, some bromo-nitro-DHA, and a trace of monobromo- DHA.

EXAMPLE 3 Morzo-iodz'nation of DHA In a 2-liter resin kettle fitted with mechanical stirrer and long reflux condenser was placed 898 grams of methylene chloride. To this was added 337 grams (0.5 mole) of DHA, not all of which dissolved. Next, 66.7 grams of iodine (0.2625 mole) was added, followed by 91.5 grams of nitric acid (99 percent) to make a 2 molar acid solution. The reaction mixture was refluxed for 16 hours at 43 to 45 C., this temperature being maintained automatically by the evaporation and condensation of the methylene chloride. At the end of the 16 hour period 57.0 grams of 99 percent nitric acid was added, bringing the calculated acid concentration up to 3 molar. The reaction mixture was refluxed for 4 hours more and was then worked up by the procedure set forth in Example 1 or hexachlorobutadiene.

above. The residual product weighed 390 grams and consisted essentially of mono-iodo-DHA, a yield equivalent to 97.5 percent of the theoretical obtainable.

EXAMPLE 4 Di-iodination .0 DHA In a 4-liter resin kettle fitted with mechanical stirrer and double reflux condenser was placed 1795 grams of methylene chloride. To this was added with stirring 674 grams (1 mole) of DHA. Next was added 280 grams (approximately 1.1 mole) of iodine, and finally 291 grams of white fuming (99 percent) nitric acid, making the calculated acid concentration 3 molar. The reaction mixture was heated at reflux temperature (43 to 45 C.) for 16 hours, at the end of which time the calculated acid concentration was increased to 4 molar by the addition of 114 grams of 99 percent nitric acid. Refluxing was then continued for an additional period of 24 hours. The reaction mixture was then Worked up as in Example 1. There was recovered from the residual'product a total of 750 grams of di-iodo-DHA, equivalent to 81 percent, based on the weight of the DHA employed in the reaction. The remainder was iodo-nitroDHA.

EXAMPLE 5 Bromonitration of DHA The monobr-omination of DHA described in Example 1 was repeated, and with the same quantities of reactants used therein, up to the point where monobromination was complete. The calculated acidity of the reaction mixture was then increased to 7 molar by the addition of 270 grams of 99 percent nitric acid. Refluxing was then continued for 4 hours. The reaction mixture was then worked up as in Example 1. The residual product contained a total of 780 grams of bromo-nitro-DHA, equivalent to 98 percent of the theoretical yield, based on the weight of DHA employed in the reaction.

EXAMPLE 6 Iodonitralion of DHA The mono-iodination of DHA described in Example 3 Was repeated, and Wit-h the same quantities of reactants used therein, up to the point where m-ono-iodination was complete. The calculated acidity of the reaction mixture was then increased to 7 molar by the addition of 270 grams of 99 percent nitric acid. Refluxing was then continued for 1 hour. The reaction mixture was then worked up as in Example 1. The residual product yielded 395 grams of 2-iodo-3-nitro-DHA, equivalent to 93 percent of the theoreticaal, based on the weight of the DHA employed in the preparation.

As indicated earlier in this specification, the halogenated and halo-nitrated derivatives of DHA prepared according to the process of our invention are of commercial importance not only in themselves but also as intermediates in the preparation of other potentially valuable compounds. Of particular interest are the compounds obtained by the pyrolytic cracking of the DHA derivatives. We have found that pyrolytic cracking in a wiped-film molecular type still under reduced pressure is particularly advantageous and results in maximum yields and minimum undesired decomposition.

Typical conditions we have employed for carrying out the pyrolytic cracking are as follows: The DHA derivative to be cracked is dissolved in a solvent such as methylene chloride or is slurried with a suitable carrier liquid such as the liquid chlorinated naphthalenes and diphenyls, In any case, the solvent or carrier liquid must be inert toward the product of pyrolysis and thermally stable at the cracking temperatures employed. We prefer in general to employ a slurry using about 3 to 5 or more parts by weight of hexachlorobutadie-ne to 1 part of the DHA derivative, the proportions being adjusted to provide proper fluidity for satisfactory still operation. The cracking still is heated to and maintained at an outside wall temperature of about 375 to 450 C., and is operated preferably under reduced pressure of the order of 20 to 30 inches of vacuum. Maintenance of Pyrolytic cracking under these conditions of the halogenated and halo-nitrated derivatives of DHA prepared according to the examples given above results in the formation of the corresponding halogenated or halo-nitrated derivatives of naphthalene and the regeneration of hexachlor-ocyclopentadiene used originally in the formation of the DHA. Thus, in addition to the regeneration of the hexachlorocyclopentadiene in all cases, the pyrolytic cracking accomplishes the conversion of the monobromo- DHA of Example 1 to Z-br-omonaphthalene; the dibromo- DHA of Example 2 to 2,3-dibromonaphthalene; the monoiodo-DHA of Example 3 to 2-iodonaphthalene; the diiodo-DHA of Example 4 to 2,3-di-iodo-naphthalene; the 2-bromo-3-nitro-DHA of Example 5 to 2-bromo-3-nitronaphthalene; and the 2-iodo-3-nitro-DHA of Example 6 to 2-iodo-3-nitronaphthalene.

To the best of our knowledge, 2,3-di-iodonaphthalene, prepared from di-iodo-DHA as described above, has never been prepared hither-to by any method. 2,3-di-iodonaphthalene may be used, for example as a dyestuif intermediate and in the formulation of pesticides.

All modifications and ramifications of our invention which will naturally suggest themselves to one skilled in the art as -a result of the disclosure in this application are deemed to be comprehended within the scope of this invention as limited only by the claims.

We claim:

1. A process for preparing a mono-halogenated and mono-nitrate-d derivative of the Diels-Alder adduct, 1,2,3, 4,5,6,7,8,13,l3,14,14 dodecachloro 1,4,4a,4b,5,8,8a,12b octahydro-1,4;5,8-dimethanotriphenylene, comprising reacting said adduct with a halogen taken from the class consisting of bromine and iodine in a solution of fuming nitric acid in methylene chloride, the mole ratio of the halogen to the adduct being about 1:2, and the concentration of the nitric acid being not greater than about 3 molar, and thereafter increasing the concentration of the nitric acid to about 7 molar.

2. The process of claim 1, the fuming nitric acid being white fuming nitric acid containing about 98 to 100% HNO 3. The process of claim 1, the temperature at which the halogenation is effected being maintained automatically below C. by the refluxing of the methylene chloride.

4. The process of claim 1, the halogen being bromine. 5. The process of claim 1, the halogen being iodine.

References Cited by the Examiner UNITED STATES PATENTS 2,658,913 11/1953 Hyman et .al. 260-646 X 3,065,278 11/1962 Cheifetz et a1. 260645 OTHER REFERENCES Danish et al.: I. Am. Chem. Soc., vol. 76, pp. 6144- REUBEN EPSTEIN, Primary Examiner.

CARL D. QUARFORTH, Examiner. L. A. SEBASTIAN, Assistant Examiner. 

1. A PROCESS FOR PREPARING A MOMO-HALOGENATED AND MONO-NITRATED DERIVATIVE OF THE DIELS-ALDER ADDICT, 1,2,3, 4,5,6,7,8,13,13,14,14-DODECACHLORO-1,4,4A,4B,5,8,8A,12BOCTAHYDRO-1,4,5,8 -DIMETHANOTRIPHERYLENE, COMPRISING REACTING SAID ADDUCT WITH A HALOGEN TAKEN FROM THE CLASS CONSISTING OF BROMINE AND IODINE IN A SOLUTION OF FUMING NITRIC ACID IN METHYLENE CHLORIDE, THE MODE RATIO OF THE HALOGEN TO THE ADDUCT BEING ABOUT 1:2, AND THE CONCENRATION OF THE NITRIC ACID BEING NOT GREATER THAN ABOUT 3 MOLAR, AND THEREAFTER INCREASING THE CONCENTRATION OF THE NITRIC ACID TO ABOUT 7 MOLAR. 